There are 2 power modes of operation: normal and idle mode. The device operates in normal-power mode after reset. In this mode the device is fully functional, i.e. all clock domains are available and can be enabled. In normal mode, the LPC2939 consumes typically around 1.1 mA/MHz. When the clocks are switched off, it consumes around 30 µA. The system can be put into idle-power mode either partially or fully. In idle mode, selected clock domains can be switched off using the Power Management Unit, and might also suspend execution of the software. The clock domains are enabled again upon a wake-up event. This wake-up event is provided by the Event Router. The clock domains that can be switched off during idle-power mode depend on the selected wake-up events. For an external interrupt (e.g. EXTINT0), no active clock is required, i.e. all clock domains can be switched off. However, for wake-up on a timer interrupt, the clock domain of the timer should stay enabled during low-power mode. In general, each subsystem that might cause a wake-up upon an interrupt must be excluded from the low power mode.